Getting a modem working under Redhat Linux

(This page was written for Redhat 6.2 and 7.0, but may still apply.)

Redhat Linux isn't generally oriented toward home machines, and doesn't install modems easily like the more home-oriented distributions (e.g. SuSE). Nor do they offer a shred of help on their support site for modem configuration. On the other hand, Redhat seems to offer better support for graphics cards, monitors, and SCSI controllers than SuSE does.
If you want to use Redhat and need to use a modem for PPP, here's how I got mine working:

First, if you have a winmodem, you may be out of luck. Support for winmodems needs to come from the manufacturer, and most manufacturers don't support linux yet. If you're not sure whether your modem is supported, or you want to know what modem to buy for a linux machine, or for more details on the state of winmodem support under linux, check the excellent Linux and Modems page.

These instructions assume that you have an ISA modem which is not a winmodem. Most PCI modems are winmodems; if you have one which is not, please add to this page and share your knowledge!

If you're lucky enough to have an old modem with jumpered settings for IRQ, you can skip the next step. If you have a PnP modem:

As root:

pnpdump > /etc/isapnp.conf
vi /etc/isapnp.conf
Now pick one of the settings to uncomment, and also uncomment the ACT Y line at the end.
isapnp /etc/isapnp.conf
until isapnp reports success.

Now, you'll have to change the permissions on the modem lines (for some reason, redhat makes these only available to root).

chmod 666 /dev/ttyS*

You'll also have to change the permissions on the ppp daemon to make it setuid, in order to run PPP as non-root:

chmod +s /usr/sbin/pppd

Now, as yourself, you need to set up a PPP account. I strongly recommend kppp. Redhat's new tool, rp3 and rp3-config (the tool you get if you do Internet->Dialup Configuration Tool, except that rp3 only works as root yet you're not supposed to be running X as root, go figure), probably also work, but I found them harder to use, and they don't give you the option to test the modem and see if it's working. So use kppp and get the modem working, then if you prefer to use rp3 to run ppp, go ahead.

kppp &
and set up the following tabs:
  DEVICE tab
    (Select appropriate /dev/tty entry depending on which entry
     you uncommented in isapnp.conf.)

  MODEM tab
    Click on QUERY MODEM
If you see: "Can't create lock file", then you need to do, as root:
  chmod 777 /var/lock
If you see: "Sorry, the modem is busy", try this:
  setserial /dev/ttyS1 autoconfig
(or S0 if that's where your modem is) I find I have to run setserial every time I boot the machine; so I edited one of the scripts under /etc/init.d and added the command there.
Linux links page
Shallow Sky home